1) Field of the Invention
The present invention relates to an ambient light detector, a laser lighting control device using the same suitable for use in a bar code reader, and a bar code reader.
2) Description of the Related Art
FIG. 20 is a block diagram showing the configuration of a bar code reading device (bar code reader). Referring now to FIG. 20, numeral 31 represents a bar code printed on a surface of an article, the bar code being formed of plural black bars and white bars arranged alternately. A predetermined datum is represented based on the width of each black bar and the width of each white bar.
An optical system (laser scanner device) 32 irradiates a laser beam L2 to the bar code 31 and receives a reflected light R1 of the laser beam L2 reflected by the bar code 31. The optical system 32 also is constituted of a laser emitting unit 33, a scanning mechanism 34 and an optical converting unit 35. The laser emitting unit 33 includes a semiconductor laser for emitting a laser beam L1.
The scanning mechanism 34 is constituted of a polygon mirror that is rotatably driven with, for example, a motor. The scanning mechanism 34 also irradiates the laser beam L1 to the plural black bars and white bars forming the bar code 31, the beam L2 formed by reflecting the laser beam L1 from the laser emitting unit 33, while it moves and scans the laser beam at a fixed rate in the direction perpendicular to the black and white bars of the bar code 31.
The scanning mechanism 34 irradiates the reflected beam R1 as the reflected beam R2 to the photoelectric converting unit 35, the reflected beam R1 being the laser beam L2 reflected by the bar code 31 and traveled with the laser beam L2 scanned.
The photoelectric converting unit 35 is formed of a photoelectric converting element, for example, a photo diode. The photoelectric converting unit 35 also receives the reflected light R2 (light input signal) via the scanning mechanism 34 to convert it to an electric signal (analog value) corresponding to the light amount thereof.
Numeral 36 represents an A/D converter unit which digitize an electrical signal from the photoelectric converting unit 35. The A/D converter unit 36 digitizes the electric signal from the photoelectric converting unit 35 to convert it to a binary signal including a black level signal corresponding to each black bar portion and a white level signal corresponding to each white bar portion in the bar code 31. The white level signal represents a high level signal and the black level signal represents a low level signal because the light amount of the light R2 reflected by each white bar portion is larger than that of the light R2 reflected by each black bar portion in the binary signal.
Numeral 37 represents a bar width counter which counts clock signals from the clock generator 38. The bar width counter 37 also outputs as clock signal count value the time widths of the black level signal portion and the white level signal portion of a binary signal from the A/D converter unit 36, or each black bar width and each white bar width of an actual bar code 31.
Furthermore, the memory 39 stores the bar width count value from the bar width counter 37. The CPU 40 extracts and demodulates predetermined data having the bar code 31 based on the bar width count value (a value corresponding to each black bar width or each white bar width) stored in the memory 39.
In the above structure, the scanning mechanism 34 irradiates the laser beam L1 as the laser beam L2 emitted from the laser emitting unit 33 to the black bar and the white bar of the bar code 31 while it moves and scans the laser beam at a constant rate and in the direction perpendicular to the black bar and white bar of the bar code 31.
The laser beam L2 emitted from the scanning mechanism 34 is scatteringly reflected on a portion of the bar code 31 and is re-irradiated as the reflected light R1 to the scanning mechanism 34. The reflected light R1 varies its reflection angle as the laser beam L2 scans and moves. However the polygon mirror constituting the scanning mechanism 34 reflects the reflected light R1 to input it as the reflected light R2 to the photoelectric conversion element in the photoelectric converting unit 35 arranged at a predetermined place.
The photoelectric converting unit 35 converts the reflected light R2 to an electric signal corresponding to the light amount thereof. The A/D converter unit 36 digitalizes the electric signal into a binary signal including a black level signal corresponding to each black level portion and a white level signal corresponding to each white level portion of the bar code 31.
Then, the bar width counter 37 counts the clock signals from the clock generator 38 to measure as a clock signal count value the time width (values corresponding to the widths of each black level signal portion and each white level signal portion in an actual bar code 31) of the black level signal portion and the white level signal portion of a binary signal from the A/D converter unit 36. The memory 39 stores temporarily the count value. The CPU 40 subjects the bar width count value stored in the memory 39 to a predetermined demodulation process to extract and demodulate the determined data of the bar code 31.
In the binary device used for the bar code reader, noises with higher frequency components are attenuated through an integration operation to improve the bar width detection accuracy.
In comparison with the He-Ne gas laser, the semiconductor laser in the laser emitting unit 33 is smaller and operates at a lower power consumption. However there is a problem that its operational life is short.
To cope with the above problem, various proposals have been made to prolong the serviceable life of the semiconductor laser used for the laser bar code reader.
For example, according to a proposal, a laser is turned off when a reading operation is not performed for a fixed period of time and then it is re-activated by a means at a re-reading operation time. As the means, a method has been considered, for controlling an activation/suspension by an operator's button switching operation, or for controlling an activation/suspension by detecting bar code information from an operator based on a presence or absence of the reflected light of an LED emitting light.
However, as described above, there is a problem in providing an improved operability and automated system because the push button switching system, for example, requires an explanation on how the bar code operates and how to control the bar code reader to an operator.
Moreover in the reflection-type sensor system using a reflected LED light, there is a disadvantage in that the position to mount the LED is limited and taking the operational life of the LED in account causes higher manufacturing cost.